1. Field of the Invention
The present invention relates to brake actuators for coupling vehicles with trailers and other towed transports having pneumatic brakes. More specifically, the invention is a heavy duty design for a brake actuator with structural enhancements to increase ruggedness and reliability over others presently on the market.
2. Description of the Background
There are a wide variety of commercially-available couplings incorporating brake actuators for utility trailers, boat trailers and the like which trailers are equipped with conventional pneumatic wheel brakes. The brake actuators serve to apply the brakes of the trailer as the trailer approaches the pulling vehicle. During towing, when the pulling vehicle decelerates by applying its brakes, the inertia of the trailer causes a forward force upon the towing vehicle. The trailer begins to override the towing vehicle. When this occurs, the trailer brake actuator applies the trailer brakes to reduce the force of inertia in the trailer. This greatly reduces the amount of work required for the pulling vehicle""s brakes to stop the trailer. When the pulling vehicle accelerates, or remains at constant speed, the inertia and/or drag of the trailer is responsible for creating a tensile force between the trailer and pulling vehicle. This tensile force deactivates the actuator; hydraulic pressure to the brakes is released and braking is eliminated. This allows the actuator to function only when the trailer is forcing the pulling vehicle forward and not when the pulling vehicle is pulling the trailer.
The design of most trailer brake actuation systems is to have an outer casing which is connected to the trailer, and an inner casing which is to be telescopically operated within the outer casing connected to the pulling vehicle. A typical design for the outer casing is to have complicated geometry and to be formed as a welded assembly of components. It is the telescopic action of the inner casing relative to the outer casing that actuates the master cylinder, which is responsible for hydraulically activating the trailer brakes. For example, U.S. Pat. No. 3,783,982 to Wells discloses a telescoping tongue and brake actuator assembly for brake-equipped trailers which can be extended without disconnecting the braking structure. A motion dampening spring 76 is included. However, the illustrated coupling employs a simple telescoping square-beam design that is subject to frictional wear and tear. Over time it has been found that the wear and tear impedes the cooperation of the parts and eventually causes catastrophic stress fractures. This design has in the past been successful for light duty environments and/or highway conditions in the application of the brakes, thereby preventing the forward force created by the trailer""s inertia upon the towing vehicle. But under heavy loading, rough environment, or off road conditions, and over extended periods of operation these systems presented problems that were never perfected, only remedied by the frequent replacement of these units. These devices presented strength and durability flaws focused upon, in general, the outer casing and/or inner casing. Buckling or bending of these components is common therefore the initial strength of these components is of concern. The telescopic action between the inner casing and outer casing is also of concern. This telescopic action is accomplished in general by the sliding of the outer casing over the inner casing. It is this sliding action that creates problems due to the extreme friction created between the casings. Over time, this friction wears away the walls of the inner and outer casings, substantially weakening these components as well as increasing the amount of clearance between the components, thereby causing them not to fit tight enough. This xe2x80x9cslopxe2x80x9d adds substantially to the strength problems already discussed herein above.
Partial solutions to the above-described situation have been suggested. For instance. U.S. Pat. No. 5,013,059 to Goettker shows a brake actuator/coupler in which a square inner casing 46 fits within a square outer casing 18, and pins 8 through oblong slots 70, 72, 74 and 76 give a sliding degree of freedom. Rollers are used to reduce friction. Specifically, a front roller 40 and rear rollers 42 protrude through inner casing 46 and bear against outer casing 18 to facilitate sliding. A single damping shock absorber 84 is used. While the use of rollers helps, there are still significant torsional stresses and wear and tear issues that renders the design unsuitable for many heavy-duty industrial applications. Even with the rollers, wear and tear over time introduces significant tolerances that can leave the rollers ineffective. Consequently, this and like designs continue to fail after prolonged use on test tracks.
Accordingly, there remains a significant need for a more rugged coupling design that combines a sturdier telescoping casing with adjustable rollers to compensate for wear and tear tolerances. The additional use of plural damping shocks and other structural enhancements are capable of giving a level of ruggedness and reliability that far exceeds other coupling/brake actuator units presently on the market.
It is, therefore, an object of the present invention to provide a heavy duty trailer coupling with integral brake actuator that employs a sturdier telescoping casing and rollers to compensate for wear and tear tolerances.
It is another object to provide adjustable rollers for adjustment of the telescoping inner and outer casings to compensate for increased wear tolerances over time.
It is another object to incorporate a damping system inclusive of plural damping cylinders between the telescoping inner and outer casings, plus a damped master brake cylinder.
It is another object to provide heavy duty inner and outer casings, the inner casing being welded to control tighter tolerances.
In accordance with the above objects, an improved heavy duty trailer coupling with integral brake actuator is provided. The trailer coupling/brake actuator generally comprises a hollow tubular outer beam, and an inner case formed as a section of hollow I-beam and adapted for a telescoping fit inside the outer case. The outer casing may be made from a single piece of reinforced square tubing. Having a solid rolled tube as the basis for the actuator greatly increases the strength of the actuator. The outer casing is reinforced by welded steel straps on the outside, and this increases its strength as well.
The inner casing is made from a welded assembly in the shape of a double I-beam. Tight tolerances are kept to ensure that the desired distance is kept between the inner and outer casing. This increases the strength of the inner casing and provides a surface for which the rollers can run on as described.
A plurality of rollers are secured to the sides of the outer case and projecting inwardly to provide bearing support against the outwardly-projecting lateral ridges of the I-beam, and this results in a substantially frictionless telescoping extension. Each of the rollers preferably comprises a wheel mounted on a selectably-offset axle to allow adjustment of the degree of support against the lateral ridges of the I-beam. This adjustment feature allows compensation for increased wear tolerances over time.
A master pneumatic brake cylinder is mounted inside the outer case for engagement with the inner case.
A safety release assembly is provided, and this includes a chain coupled at one end to the towing vehicle and coupled at the other end to a break-away lever that is pivotally mounted atop the outer case and is in operative engagement with the master cylinder. This way, inadvertent separation of the towing vehicle from the coupling/brake actuator activates the master cylinder to apply the trailer brakes to prevent accidents.
In addition, an improved damping configuration is provided. Specifically a plurality of master pins are inserted through corresponding grooves through the side walls of the inner case. A pair of damping cylinders are pivotally anchored inside the inner case and each has a piston rod attached to a corresponding one of the master pins. The pneumatic master cylinder for actuating the trailer brakes is separately damped. The pneumatic master cylinder is mounted inside the outer case and has a piston operatively engaged with the inner case for applying the trailer brakes. The pneumatic master cylinder is mounted in the outer case on spring-brackets to provide overload protection. In this regard the spring-brackets engage upon excessive pressure applied to the hydraulic system.